Just wanted to share my experience if it ever can help anyone who ever has to go through this.
My parent's/family dog Mandy was diagnosed with a brain tumour three years ago. We were told there was not treatment possible and it was inoperable.
It is inoperable-that much is true (it's a brain stem tumour).
However there is one centre in Canada (it was in Saskatoon but has moved temporarily to Calgary) and I'm sure they are opening up elsewhere-that treats cancer in pets! (the centre that treated our dog treated cats and rabbits too).
They do radiation and/or chemo and I think it's imperative that when your dog (or any other pet) is given a 'no chance' outcome to phone around, search on the internet and see what other options there are. Just like Dr.'s vets don't always know about every option. So keep your mind open and look around!
The centre she was treated at was wonderful. They usually treat pets who come from other cities and are totally set up for that. You get a call EVERY day to tell you how they are doing. They wander free in the clinic after their treatment and socialize with the vets there. They go home every night with a vet or vet student. Mandy did not want to leave when her treatment was up-it was a very home like environment. They even sent us pictures of her dressed up as a vet for halloween and we still visit when we go through that province.